This invention relates to power transmission lines in general and more particularly to a circuit arrangement for determining the reactance of a power transmission line in the event of a short circuit.
In selective protection engineering, it has been known for a long time that the distance of the fault location from the installation site can be determined by measurement of the resistance of a power transmission line between the installation site of a protective arrangement and the location of a fault, since the resistance is proportional to the distance. It is further known from the literature to measure the reactance of the power transmission line between the installation site of the protective arrangement and the short circuit; if the reactance is measured, it has the advantage that the determination of the short circuit location is only slightly influenced by the arc resistance or by the resistance to ground. The reactance Xk of a power transmission line can be described by the following equation: ##EQU1## In this equation .vertline.Uk.vertline. gives the peak value of the short circuit voltage on the transmission line and .vertline.Ik.vertline. the peak value of the short circuit current in the transmission line as measured at the installation site of the protective arrangement; the phase angle between the short circuit voltage and the short circuit current is designated as .phi. k.
In order to determine the reactance of the line in the event of a short circuit for determining the location of the short circuit on a power transmission line, it is therefore necessary to determine .vertline.Uk.vertline., .vertline.Ik.vertline. and sin .phi. k as well as to interlink these variables mathematically. With the present state of the art in electronic circuits, this can be done without difficulty if sufficient time is provided therefor.
It is an object of the present invention to provide a circuit arrangement for determining the reactance of a power transmission line in the event of a short circuit, by which the reactance and therefore also the short circuit can be determined in a very short time from the measurement variables .vertline.Uk.vertline. and .vertline.Ik.vertline.; this is desirable so that the reactance and therefore also the short circuit can be determined exactly and with certainty in the short time period before the following circuit breakers open, after an excitation circuit has responded in the event of a short circuit or an associated protective device has delivered a tripping signal.